1. Field of the Invention
The present general inventive concept relates to a method of centering a disk of a hard disk drive (HDD), and more particularly, to a method of centering a disk of an HDD by which a disk or a spacer may be easily assembled on a hub, a time of centering may be relatively much reduced, and a superior centering quality may be obtained.
2. Description of the Related Art
Hard disk drives (HDDs) are memory devices formed of electronic apparatuses and mechanical apparatuses for recording and reproducing data by converting a digital electronic pulse into a permanent magnetic field. The HDD is widely used as an auxiliary memory device for a computer system because it can access a large amount of data at high speed.
The HDD may include a disk stack assembly having a disk for recording and storing data, a head stack assembly (HSA) for reading out data from the disk by pivoting across the disk around a predetermined pivot shaft, a printed circuit board assembly (PCBA) for controlling the above constituent elements by mounting most circuit parts on a printed circuit board (PCB), a base on which the above constituent elements are assembled, and a cover for covering the base.
Imbalance in a rotating system such as a head stack assembly or a disk stack assembly is an amount of imbalance generated by eccentrically distributed mass of a rotary body with respect to each rotation center. The imbalance generates vibrations and noise during rotation. Especially, in a disk stack assembly, the eccentricity of a disk damages a ball bearing or a fluid bearing of a spindle motor so that reliability of an HDD may be deteriorated. Also, the imbalance has an ill effect on a servo track write (STW) process in a manufacturing process of an HDD.
Although there are various reasons for generation of imbalance in the disk stack assembly, due to tolerance of constituent elements such as a spindle motor, a disk, or a spacer constituting the disk stack assembly, the rotation center of each of the constituent elements does not match a weight center to the rotation center of assembled constituent elements in the assembly of the constituent elements so that imbalance may be generated due to the eccentricity.
Many studies on technologies to improve the imbalance of a disk stack assembly have been performed and some of the technologies are introduced herein.
First, a spacer or a disk is pushed to one side and a displacement is measured. Then, the spacer or disk is pushed in the opposite direction by half of the measured displacement so that alignment may be achieved.
Second, when disks are assembled on a hub, the amount of imbalance between the disks and the hub is measured. By giving an impact to one side of a disk, a state in which the amount of balance is the minimum is obtained. This is referred to as a dynamic imbalance method.
Third, when a plurality of disks are assembled, one disk is pushed to one side whereas another one is pushed to the opposite side. Thus, the disks are assembled in a zigzag or biased form so that the amount of imbalance is reduced in terms of probability.
Fourth, the amount of imbalance is measured during assembly of a disk, and mass balance is added to a side having a relatively less.
The above methods are used because making tolerance between the hub and the spacer tight in order to continuously stack a plurality of disks is difficult. In detail, when the tolerance is made too tight, the centering process may not be needed by greatly reducing the amount of imbalance.
However, when the tolerance of the hub, the disk, and the spacer is made tight, it is difficult to push the spacer and the disk down to the lower portion of the hub, that is, the bottom side, to sequentially stack the spacer and the disk. If the spacer and the disk are forcibly pushed down, scratches or cuts may be highly likely to be generated on the hub.
The scratches and cuts may generate particles and then the particles may scratch the disk so that the quality of an HDD may be badly affected. Also, when the spacer and the disk are forcibly pushed down as described above, a degree of flatness of a surface of the spacer during stacking the spacer and the disks is affected so that the quality of STW, that is, repeatable run out (RRO) or non-repeatable run out (NRRO), may be badly affected.
In the above-described conventional method for centering a disk of an HDD, imbalance is reduced not by accurately performing the centering of a disk by allowing the hub, the disk, and the spacer to have tight tolerance, but by using a method of reducing the amount of imbalance by an additional process of measuring the amount of imbalance after assembly or by allowing imbalance that an HDD basically keeps, to a degree. As a result, the quality characteristic of each of the HDDs varies due to an assembly state and thus there is a certain limit in productivity and improvement of a recording characteristic. Until now, the limit has been overlooked due to the problem in the assembly of a disk as described above.